A new cap (pictured) was lowered into place Monday over BP's gushing oil well in the Gulf, and today was temporarily sealed. For the first time in three months, oil is not gushing into the ocean from this disaster.

Don't get too excited, though. Using the cap to close off the well is just part of a series of tests, and does not mean that the Gulf will be spared future gushes. According to the New York Times:

The test commenced after two days of delays while BP fixed a leak in the equipment that engineers discovered on Wednesday night. Engineers replaced equipment on the tight-sealing cap that has been placed at the top of well, 5,000 feet under water, said Kent Wells, a senior vice president of the company. The equipment, part of a choke line that was the last valve to be closed before the pressure test could begin.

BP said that its three-ram capping stack was closed, "effectively shutting in the well and all sub-sea containment systems."

Live feeds of video images from the undersea well clearly showed that the release of oil had had been completely halted.

Mr. Allen, clarified the role of the cap in his news conference on Thursday morning, saying that this mechanism was never meant to be the ultimate solution to closing the well.

Mr. Allen called it a "precursor" to containment, making it possible for the gushing crude to be captured through four different systems that together can keep up with the estimated rate of flow, which the government now puts at 35,000 to 60,000 barrels a day. If all goes well, it may also be used to seal the well completely for brief periods.

"I don't want to reverse the priorities here, because the priority was to contain and stop the flow of oil," he said, "but the design of the cap itself, if we can withstand the pressures and the well bore stays intact, presents the opportunity to shut the well in, which will give us the ability to abandon the site in a hurricane, so it's a two-for if we can do it."

The test involves closing all the valves on the new cap, which was installed earlier in the week, to increase pressure in the well so that BP can assess its condition over the length of the well bore, which extends 13,000 feet below the seabed.

Mr. Allen likened the process to putting a thumb over the end of a running garden hose. If the pressure does not rise as a result, that means there is a leak somewhere. In the case of the well, if the resulting pressure is high, that means the well bore is intact, he said.

Here is how this new cap will work during testing:

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For a better understanding the various caps that BP has tried, you can look at some incredibly helpful diagrams on the NY Times website. Even when a permanent cap has been placed on the well, the disaster isn't over. We will still be coping with profound environmental damage and cleanup.